Preventing cracking of silicon steel during hot rolling



Patented Nov. 25, 1952 UNITED STATES rarest o ies PREVENTING CRACKING OF SILICON STEEL DURKNG HOT ROLLING New Jersey No Drawing. Application November 21, 1949, Serial No. 128,6 8

1 Claims. 1

This invention relates to the prevention of cracking of silicon steel during hot rolling and more particularly to cracking of electrical steel containing from 2. to 2.4% silicon While rolling ingots into slabs.

Electrical steels of the grade containing from 2. to 2.4% silicon have been unduly expensive to produce due to severe cracking during rolling of the ingots into slabs, i. e., slabbing. This cracking carries over into the finished product and causes a poor surface condition in a good share of the product resulting in such product being unsuitable for its intended purpose. Heretofore, the only way of preventing such cracking was by breaking down the ingots, reheating and then rolling into slabs of the desired size. In this practice, the ingot is given two or three light passes on the slabbing mill, returned to the soaking pits for reheating and soaking prior to rolling into a slab. This practice is quite costly due to the double heating involved and moreover reduces production due to double use of the pits and extra rolling time.

It is accordingly an object of this invention to provide a simple and economical method of preventing cracking of the foregoing grade of silicon steel during hot rolling and slabbing thereof.

It is a further object to provide a method of preventing such cracking which does not deleteriously affect the electrical properties of the steel.

I have discovered that the foregoing objects can be attained by increasing the phosphorus content of the steel above the 015% maximum heretofore standard for such steel to between .05 and .15% and preferably to between .06 and Steel of the 2. to 2.4% silicon grade has the following analysis:

Per cent Carbon maX .06 Silicon 2 to 2.4 Manganese .25 to .85 Sulphur rnax .02 Copper 0 to .12

Ordinarily this steel has a maximum phosphorus content of 015% but in accordance with the preferred teachings of my invention, the phosphorus content is raised to .06 to 08% by the addition of ferro-phosphorus to the molten steel. This can conveniently be done in the ladle. Since no reladling is necessary with this grade of steel, the ferro-phosphorus may be added either to ferro-silicon placed on the bottom of the ladle before tapping or introduced into the stream of metal during tapping.

The steel is otherwise made and treated in accordance with conventional practice. It is preferably refined in a basic open hearth and the carbon reduced therein to at least 06%. Followthis, it is tapped into a ladle where it is alloyed with silicon and phosphorus and teemed into suitable molds. After solidifying, it is reheated to between 2200 and 2300 F. and rolled in a slabbing mill, the finishing temperature being not less than 1875 F. The slabs are then cooled to room temperature, reheated to about 2250 F. and hot rolled to strip about .08" thick and coiled. After pickling, the strip is cold reduced to gauge and annealed.

As a result of the phosphorus addition, the slabs are free from cracks and the cold-rolled strip has the desired smooth surface. Moreover, as is shown by the following tabulation, .25" gauge sheets easily meet the guarantee of a maximum watt loss of 1.50 watts per pound at 10 kilogausses and 60 cycles.

10 kilogausses Average 1.25

Thus, it is apparent that by the addition of up to .15% and preferably between .06 and 08% phosphorus freedom from cracking without harming the electrical properties of the 2. to 2.4% silicon steel is efiected.

I claim:

1. The method of preventing cracking of the 2. to 2.4% grade of silicon steel containing 06% maximum carbon during slabbing thereof comprising adding ferro-phosphorus to the molten steel during ladling thereof, the ferro-phosphorus being added in an amount to provide a phos phorus content of between .05 and 15% in the finished steel, casting ingots from said steel, heating said ingots to between 2200 and 2300 F. and rolling said ingots to slabs in a slabbing mill, said rolling being completed at a temperature not less than 1875" "R, said phosphorus content and the temperature of said rolling combining to prevent edge cracking of said ingots by said rollmg.

2. The method of preventing cracking of the 2. to 2.4% grade of silicon steel containing .06% maximum carbon during slabbing thereof comprising adding ferro-phosphorus to the molten steel during ladling thereof, the ferro-phosphorus being added in an amount to provide a phosphorus content of between .06 and 0.8% in the finished steel, casting ingots from said steel,

heating said ingots to between 2200 and 2300 F.

and rolling said ingots to slabs in a slabbing mill, said rolling being completed at a temperature not less than 1875 F., said phosphorus content and the temperature of said rolling combining to prevent edge cracking of said ingots by said rolling.

3. The method of preventing cracking of the 2. to 2.4% grade of silicon steel containing .06% maximum carbon during slabbing thereof comprising adding ferro-phosphorus to the steel while molten in an amount to provide a phosphorus content of between .05 and 15% in the finished steel, casting ingots from said steel, heating said ingots to between 2200 and 2300 F. and rolling said ingots to slabs in a slabbing mill, said rolling being completed at a temperature not less than 1875 F'., said phosphorus content and the temperature of said rolling combining to prevent edge cracking of said ingots by said rolling.

4. The method of preventing cracking of the 2. to 2.4% grade of silicon steel containing .06% maximum carbon during slabbing thereof comprising adding ferro-phosphorus to the steel while molten in an amount to provide a phosphorus content of between .06 and .08% in the finished steel, casting ingots from said steel, heating said ingots to between 2200 and 2300 F. and rolling said ingots to slabs in a slab-bing mill, said rolling being completed at a temperature not less than 1875 F., said phosphorus content and the temperature of said rolling combining to prevent edge cracking of said ingots by said rolling.

' GEORGE H. GOODSELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,686,223 Armstrong 2 Oct. 2, 1928 2,087,766 Forbes et a1. Jul3 20, 1937 2,241,270 Nipper May 6, 1941 FOREIGN PATENTS Number Country Date 350,919 Great Britain June 10, 1931 420,543 Great Britain Dec. 4, 1934 OTHER REFERENCES The Journal of the Iron and Steel Institute, No. l, 1939, pages 181A and 182A; 7 l V 

1. THE METHOD OF PREVENTING CRACKING OF THE
 2. TO 2.4% GRADE OF SILICON STEEL CONTAINING .06% MAXIMUM CARBON DURING SLABBING THEREOF COMPRISING ADDING FERRO-PHOSPHORUS TO THE MOLTEN STEEL DURING LADLING THEREOF, THE FERRO-PHOSPHORUS BEING ADDED IN AN AMOUNT TO PROVIDE A PHOSPHORUS CONTENT OF BETWEEN .05 AND .15% IN THE FINISHED STEEL, CASTING INGOTS FROM SAID STEEL, HEATING SAID INGOTS TO BETWEEN 2200 AND 2300* F. AND ROLLING SAID INGOTS TO SLABS IN A SLABBING MILL, SAID ROLLING BEING COMPLETED AT A TEMPERATURE NOT LESS THAN 1875* F., SAID PHOSPHORUS CONTENT AND THE TEMPERATURE OF SAID ROLLING COMBINING TO PREVENT EDGE CRACKING OF SAID INGOTS BY SAID ROLLING. 